Lean Manufacturing: Eliminating the 8 Hidden Wastes – Part 6 of 8. The I in DOWNTIME

Inventory waste is any material in excess of the one piece required for the next step in the process and can be found in any of three states-raw materials, work-in-progress, and finished goods. Unless the product is being worked on and having value added to it, or it is on its way to the customer, it is inventory. Excess inventories hide many unwanted conditions. Excessive inventory may cover up quality problems like rework and defects, manpower and/or production scheduling problems, excessive lead times and supplier or vendor problems. It is very expensive to carry excessive inventory which requires capital to be tied up in interest payments. Excessive inventory reduces ROI on manpower and raw materials.

LOOK FOR inventory held “just-in-case” problems arise, or unreliable shipments from suppliers or for excessive service capability or excessive inventories with less than 12 turns per year. Also look for large lot production, unreliable forecasts, poor scheduling, poor market forecasts, unbalanced workloads, poor communications and management decision issues any of which result in increased labor, fuel, space and/or maintenance costs and material aging and risk of obsolescence.

Just-in-time manufacturing is a strategy used to reduce costs by reducing the in-process inventory level. It is driven by a series of signals that tell the production line to make the next piece for the product and when it is needed. The signals used are usually simple visual signals, such as the absence or presence of a piece that is needed in the manufacturing process. In just-in-time manufacturing, reorder levels for certain inventory items are set and new stock is ordered only when those levels are reached. There is no overstocking of parts or items, which saves on space in the warehouse. This manufacturing strategy can lead to improvements in quality and efficiency. It also can lead to higher profits and a larger return on the company’s investment. Although this specific manufacturing strategy was created by the Toyota company in Japan during the 1970s, previous businesses used manufacturing processes that were based on similar concepts. One of the first was created by Henry Ford, whose automobile company bought materials only for its immediate needs in the manufacturing process. Ford bought only the amount of material that was needed in the production plan and planned the transportations of materials so that the flow of the product would be smooth. This created a rapid turnover and decreased the amount of money that was tied up in raw materials.

The Single Piece Flow technique allows us to make only the quantity needed to fill the hole to be “pulled” by the next operation downstream from their operation. This keeps the work-in-progress to a minimum and is usually managed with a good kanban system. Often movement of batches are minimized to the smallest number efficiently handled and eventually further reduced to Single Piece Flow.

Kanban is a scheduling system that uses signals to help determine what to produce, when to produce it, and how much to produce. It is not an inventory control system. It works from upstream to downstream in the production process (i.e., starting with the customer order). At each step, only as many parts are withdrawn as necessary, ensuring that only what is ordered is made. The necessary part in a given process step always accompanies the signal to ensure visual control. The upstream processes only produce what has been withdrawn. This includes only producing items in the sequence in which the signals are received, and only producing the number indicated. Only the products that are 100% defect free continue on through the production line. In this way, each step uncovers and then corrects the defects that are found, before any more can be produced. The number of signals should be decreased over time. Minimizing the total number of signals is the best way to uncover areas of needed improvement. By constantly reducing the total number of signals, continuous improvement is facilitated by concurrently reducing the overall level of stock in production.

The 5S system is a workplace organization method that greatly improves the efficiency and management of an operational area while improving morale and saving time. The five S’s stand for Sort, Set-in-order, Shine, Standardize and Sustain. 5S is often the first step in applying Lean techniques. It helps to get all of the “junk”, including materials, out of the work area and then set procedures to keep it that way.

In Cellular Layouts, production work stations and equipment are arranged in a sequence that supports a smooth flow of materials and components through the production process with minimal transport or delay. Implementation of this lean method often represents the first major shift in production activity, and it is the key enabler of increased production velocity and flexibility, as well as the reduction of capital requirements.